Research On Metal(Metal Oxide)/Carbon Composites As Anode Materials For Lithium Ion Batteries

Carbon materials are widely used as anode materials because of its good cycle life and safety inlithium ion battery, however, its low specific capacity (372mAh/g) can’t meet the demands ofelectronic devices with high energy density, especially for the electric vehicles. As new anodematerials, Sn has a theoretical specific capacity of994mAh/g, CuO has a specific capacity of674mAh/g. Nonetheless, the large volume expansion of Sn and CuO during the charge-dischargeprocess causes pulverization of the electrodes. Therefore, the capacity decreased quickly afterseveral cycles. In order to solve this problem, Sn/C composites and CuO/graphite composites wereprepared by a simple chemical method. The phase structure and surface morphology of thematerials were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) andtransmission electron microscopy (TEM). Their electrochemical performances were characterizedby galvanostatic charge-discharge tests. The main contents and results are summarized as follows:1. Sn/graphite composites were successfully prepared via a facile chemical reduction method,using tin chloride as tin source and natural graphite as carbon source. Effects of the pH of thereaction solvent and the volume ratio of PEG-400to H2O (pure water,1:1,3:1, pure PEG) on theelectrochemical performance of the anode materials have been researched. Compared with theother Sn/graphite composites and natural graphite, the composite exhibits an initial dischargecapacity of510mAh/g and a reversible capacity of400mAh/g after50cycles, when the pH valueis6and the PEG/water volume ratio is3:1.2. Sn/CNTs composites were prepared by a facial chemical reduction method, using tinchloride as tin source and CNTs as carbon source. Based on the pH value of the above researchsystem, the structure, morphology and electrochemical performances of the products wereinvestigated via adjusting the volume ratio of PEG-400to H2O (pure water,3:1,4:1, pure PEG).The sample prepared with PEG/H2O ratio of4/1demonstrated the best performances, the firstdischarge capacity is1364.6mAh/g and the reversible capacity is540mAh/g after50cycles.3. CuO/graphite composites were synthesized by a simple calcination method, using coppernitrate as copper source and natural graphite as carbon source. The products with optimumstructure and best electrochemical performance were obtained by investigating the calcination temperature and the ratio of copper nitrate to natural graphite. These results demonstrate that theproduct shows the best electrochemical performance, when the mass ratio of copper nitrate tonatural graphite is1.5:1, and the calcination temperature is300°C. The first discharge capacity is709mAh/g, meanwhile, the capacity still remains at500mAh/g after50cycles. These resultsdemonstrate that this material exhibits a high specific capacity and good cycling stability.